We propose to investigate physostigmine, choline chloride, phosphatidylcholine, arecoline and vasopressin in patients with Alzheimer's disease, elderly subjects with an age related memory loss and young normal subjects. All of the investigational drugs were chosen because they could, through various different mechanisms, partially correct the cholinergic underactivity presumed to underly the memory deficits of elderly people and patients with Alzheimer's disease. The proposal addresses the following critical concerns: (1) That there is a curvilinear relationship between a cholinomimetic and its effects on memory and that the "therapeutic window" for the cholinomimetics to improve memory functioning is probably small. (2) That elderly people of different ages and patients with Alzheimer's disease can have very different basal levels of central cholinergic activity. Hence, a therapeutic dose could range widely from patient to patient. (3) That there is no method to conclusively diagnose Alzheimer's disease before autopsy. Two basic strategies have been offered to solve these problems. First, the proposed drug studies utilize a very broad dose range to maximize the likelihood of finding an optimal dose. And second, a series of neurochemical investigations are proposed that will attempt to assess central cholinergic activity. All these investigations use indirect methods, but all have as their ultimate goal the development of a method that could aid in the diagnosis of Alzheimer's disease and in identification of people who are more likely to respond to a cholinomimetic.